This invention relates generally to the design and fabrication of inkjet printheads, and in particular to the configuration of nozzles on inkjet printheads.
Traditionally, digitally controlled inkjet printing capability is accomplished by one of two technologies. Both technologies feed ink through channels formed in a printhead. Each channel includes at least one nozzle from which droplets of ink are selectively extruded and deposited upon a medium.
The first technology, commonly referred to as xe2x80x9cdrop-on-demandxe2x80x9d ink jet printing, provides ink droplets for impact upon a recording surface using a pressurization actuator (thermal, piezoelectric, etc.). Selective activation of the actuator causes the formation and ejection of a flying ink droplet that crosses the space between the printhead and the print media and strikes the print media. The formation of printed images is achieved by controlling the individual formation of ink droplets, as is required to create the desired image. Typically, a slight negative pressure within each channel keeps the ink from inadvertently escaping through the nozzle, and also forms a slightly concave meniscus at the nozzle, thus helping to keep the nozzle clean.
Conventional xe2x80x9cdrop-on-demandxe2x80x9d ink jet printers utilize a pressurization actuator to produce the ink jet droplet at orifices of a print head. Typically, one of two types of actuators are used including heat actuators and piezoelectric actuators. With heat actuators, a heater, placed at a convenient location, heats the ink causing a quantity of ink to phase change into a gaseous steam bubble that raises the internal ink pressure sufficiently for an ink droplet to be expelled. With piezoelectric actuators, an electric field is applied to a piezoelectric material possessing properties that create a mechanical stress in the material causing an ink droplet to be expelled. The most commonly produced piezoelectric materials are ceramics, such as lead zirconate titanate, barium titanate, lead titanate, and lead metaniobate.
The second technology, commonly referred to as xe2x80x9ccontinuous streamxe2x80x9d or xe2x80x9ccontinuousxe2x80x9d ink jet printing, uses a pressurized ink source which produces a continuous stream of ink droplets. Conventional continuous ink jet printers utilize electrostatic charging devices that are placed close to the point where a filament of working fluid breaks into individual ink droplets. The ink droplets are electrically charged and then directed to an appropriate location by deflection electrodes having a large potential difference. When no print is desired, the ink droplets are deflected into an ink capturing mechanism (catcher, interceptor, gutter, etc.) and either recycled or disposed of. When print is desired, the ink droplets are not deflected and allowed to strike a print media. Alternatively, deflected ink droplets may be allowed to strike the print media, while non-deflected ink droplets are collected in the ink capturing mechanism.
Regardless of the type of inkjet printer technology, it is desirable in the fabrication of inkjet printheads to space nozzles in a two-dimensional array rather than in a linear array. Printheads so fabricated have advantages in that they are easier to manufacture. These advantages have been realized in currently manufactured drop-on-demand devices. For example, commercially available drop-on-demand printheads have nozzles which are disposed in a two-dimensional array in order to increase the apparent linear density of printed drops and to increase the space available for the construction of the drop firing chamber of each nozzle.
Additionally, printheads have advantages in that they reduce the occurrences of nozzle to nozzle cross talk, in which activation of one nozzle interferes with the activation of a neighboring nozzle, for example by propagation of acoustic waves or coupling. Commercially available piezoelectric drop-on-demand printheads have a two-dimensional array with nozzles arranged in a plurality of linear rows with each row displaced in a direction perpendicular to the direction of the rows. This nozzle configuration is used advantageously to decouple interactions between nozzles by preventing acoustic waves produced by the firing of one nozzle from interfering with the droplets fired from a second, neighboring nozzle. Neighboring nozzles are fired at different times to compensate for their displacement in a direction perpendicular to the nozzle rows as the printhead is scanned in a slow scan direction.
Attempts have also been made to provide redundancy in drop-on-demand printheads to protect the printing process from failure of a particular nozzle. In these attempts, two rows of nozzles were located aligned in a first direction, but displaced from one another in a second direction. The second direction being perpendicular to the first direction. There being no offset between the nozzle rows in the first direction, a drop from the first row could be printed redundantly from a nozzle from the second row.
However, for continuous inkjet printheads, two-dimensional nozzle configurations have not been generally practiced successfully. This is especially true for printheads having a single gutter.
Typically, conventional continuous inkjet printheads use only one gutter for cost and simplicity reasons. In addition, occasionally all ejected drops need to be guttered. As conventional gutters are made with a straight edge designed to capture drops from a linear row of nozzles, the gutter edge in prior art devices extends in a first direction which is in the direction of the linear row of nozzles. As such, traditionally, it has been viewed as impractical to locate nozzles displaced in a second direction, substantially perpendicular from the first direction, because it would be difficult to steer or deflect drops from nozzles so located into the gutter. This is because the ability to steer or deflect drops has typically been limited to steering or deflecting of less than a few degrees; therefore, the maximum displacement of a nozzle in the second direction would be so limited that to date it has been impractical to implement.
Attempts have also been made to modify gutter shape to accommodate two-dimensional nozzle arrays. U.S. Patent application entitled Continuous Inkjet Printhead Having Serrated Gutter, commonly assigned, discloses a gutter positioned adjacent a nozzle array in one direction and displaced from the nozzle array in another direction. An edge of the gutter is non-uniform with portions being displaced or extended relative to other portions. This configuration allows the gutter to capture ink drops from a two-dimensional nozzle array. The gutter portions form a serrated profile which allow ink drops to be captured without having to deflect the ink drops through large deflection angles. When using this gutter configuration. a deflection angle of about 2 degrees is required for ink drops to be captured by the gutter. Heretofore, large deflection angles, e.g. deflection angles exceeding 5 to 10 degrees, have not been possible.
Although the above described gutter works extremely well for it intended purpose, the design of a non-uniform gutter complicates its manufacture in comparison with a gutter having a straight edge. As such, cost associated with non-uniform gutters is also increased.
The invention described in U.S. Patent Application entitled Printhead Having Gas Flow Ink Droplet Separation And Method Of Diverging Ink Droplets, filed concurrently herewith and commonly assigned, discloses a printing apparatus having enhanced ink drop steering or deflection angles. The apparatus includes an ink droplet forming mechanism operable to selectively create a ink droplets having a plurality of volumes travelling along a path and a droplet deflector system. The droplet deflector system is positioned at an angle with respect to the path of ink droplets and is operable to interact with the path of ink droplets thereby separating ink droplets having one of the plurality of volumes from ink droplets having another of the plurality of volumes. The ink droplet producing mechanism can include a heater that may be selectively actuated at a plurality of frequencies to create the ink droplets travelling along the path. The droplet deflector system can be a positive pressure air source positioned substantially perpendicular to the path of ink droplets.
With the advent of a printing apparatus having enhanced ink drop steering or deflection, a continuous inkjet printhead and printer having multiple nozzle arrays capable of providing increased printed pixel density; increased printed pixel row density; increased ink levels of a printed pixel; redundant printing; reduced nozzle to nozzle cross-talk; and reduced power and energy requirement with increased ink drop deflection would be a welcome advancement in the art.
An object of the present invention is to reduce energy and power requirements of a continuous inkjet printhead and printer.
Another object of the present invention is to provide a continuous inkjet printhead having one or more nozzle rows displaced in a direction substantially perpendicular to a direction defined by a first row of nozzles.
Another object of the present invention to provide a continuous inkjet printhead having increased nozzle to nozzle spacing.
Another object of the present invention to provide a continuous inkjet printhead that reduces the effects of coupling and cross-talk between ink drop ejection of one nozzle and ink drop ejection from a neighboring nozzle.
It is yet another object of the present invention to provide a continuous inkjet printhead that simultaneously prints ink drops on a receiver at locations displaced from other printed ink drops.
It is yet another object of the present invention to provide a continuous inkjet printhead having nozzle redundancy.
It is yet another object of the present invention to provide a continuous inkjet printhead and printer that increases the density of printed pixels.
It is yet another object of the present invention to provide a continuous inkjet printer that increases printed pixel density in a printed row by printing additional ink drops after neighboring printed ink drops have been partially absorbed by a receiver.
It is yet another object of the present invention to provide a continuous inkjet printhead and printer that increases ink levels of a pixel on a receiver.
According to a feature of the present invention, a continuous inkjet printing apparatus includes a printhead having a two-dimensional nozzle array with the two-dimensional nozzle array having a plurality of nozzles such that a redundant nozzle pair is formed. A drop forming mechanism is positioned relative to the nozzles. The drop forming mechanism is operable in a first state to form drops having a first volume travelling along a path and in a second state to form drops having a second volume travelling along the path. A system applies force to the drops travelling along the path with the force being applied in a direction such that the drops having the first volume diverge from the path.
According to another feature of the present invention, a method of redundant printing includes forming a first row of drops travelling along a first path, some of the drops having a first volume, some of the drops having a second volume; forming a second row of drops travelling along a second path, some of the drops having a first volume, some of the drops having a second volume; causing the drops having the first volume from the first and second rows of drops to diverge from the first and second paths; causing the drops having the second volume from the first row of drops to impinge on predetermined areas on the receiver; and causing the drops having the second volume from the second row of drops to impinge on the predetermined areas on the receiver.
According to another feature of the present invention, a continuous inkjet printing apparatus includes a printhead having a two-dimensional nozzle array. The two-dimensional nozzle array has a first nozzle row disposed in a first direction and a second nozzle row being disposed displaced in a second direction and aligned in the first direction relative to the first nozzle row. A drop forming mechanism is positioned relative to the nozzle rows. The drop forming mechanism is operable in a first state to form drops having a first volume travelling along a path and in a second state to form drops having a second volume travelling along the path. A system applies force to the drops travelling along the path. The force is applied in a direction such that the drops having the first volume diverge from the path.